10 research outputs found
An X-ray Image of the Composite SNR G16.7+0.1
We have observed the Galactic supernova remnant G16.7+0.1 for 13 ks using the
EPIC cameras aboard the XMM-Newton X-ray Observatory, producing the first X-ray
image of the remnant. This composite radio remnant has a core radio flux
density of only 100 mJy, making it one of the faintest radio synchrotron
nebulae yet detected, although the core-to-shell flux ratio at 6 cm is typical
of the growing class of composite remnants. Our image is seriously contaminated
by bright arcs produced by singly reflected X-rays from the X-ray binary GX17+2
which lies just outside the field of view, providing an interesting data
analysis challenge. Nonetheless, the remnant's synchrotron core is clearly
detected. We report on the spectrum and intensity of the core emission as well
as on our search for emission from the thermal shell, and describe the
constraints these observations provide on the remnant's distance, age, and
central pulsar properties.Comment: 12 pages, 4 figures. Scheduled to appear in the September 1
Astrophysical Journa
The Factory and the Beehive. II. Activity and Rotation is Praesepe and the Hyades
Open clusters are collections of stars with a single, well-determined age, and can be used to investigate the connections between angular-momentum evolution and magnetic activity over a star\u27s lifetime. We present the results of a comparative study of the relationship between stellar rotation and activity in two benchmark open clusters: Praesepe and the Hyades. As they have the same age and roughly solar metallicity, these clusters serve as an ideal laboratory for testing the agreement between theoretical and empirical rotation-activity relations at 600 Myr. We have compiled a sample of 720 spectra—more than half of which are new observations—for 516 high-confidence members of Praesepe; we have also obtained 139 new spectra for 130 high-confidence Hyads. We have also collected rotation periods (P rot) for 135 Praesepe members and 87 Hyads. To compare Hα emission, an indicator of chromospheric activity, as a function of color, mass, and Rossby number Ro , we first calculate an expanded set of χ values, with which we can obtain the Hα to bolometric luminosity ratio, L Hα/L bol, even when spectra are not flux-calibrated and/or stars lack reliable distances. Our χ values cover a broader range of stellar masses and colors (roughly equivalent to spectral types from K0 to M9), and exhibit better agreement between independent calculations, than existing values. Unlike previous authors, we find no difference between the two clusters in their Hα equivalent width or L Hα/L bol distributions, and therefore take the merged Hα and P rot data to be representative of 600 Myr old stars. Our analysis shows that Hα activity in these stars is saturated for . Above that value activity declines as a power-law with slope , before dropping off rapidly at Ro 0.4. These data provide a useful anchor for calibrating the age-activity-rotation relation beyond 600 Myr
The fifth data release of the sloan digital sky survey
Astrophysical Journal Supplement Series, 172(2): pp. 634-644.This paper describes the Fifth Data Release (DR5) of the Sloan Digital Sky Survey (SDSS). DR5 includes all survey
quality data taken through 2005 June and represents the completion of the SDSS-I project (whose successor, SDSS-II,
will continue through mid-2008). It includes five-band photometric data for 217 million objects selected over 8000 deg2
and 1,048,960 spectra of galaxies, quasars, and stars selected from 5713 deg2 of that imaging data. These numbers
represent a roughly 20% increment over those of the Fourth Data Release; all the data from previous data releases are
included in the present release. In addition to ‘‘standard’’ SDSS observations,DR5 includes repeat scans of the southern
equatorial stripe, imaging scans across M31 and the core of the Perseus Cluster of galaxies, and the first spectroscopic
data from SEGUE, a survey to explore the kinematics and chemical evolution of the Galaxy. The catalog database
incorporates several new features, including photometric redshifts of galaxies, tables of matched objects in overlap
regions of the imaging survey, and tools that allowprecise computations of survey geometry for statistical investigations
The Factory and the Beehive III: PTFEB132.707+19.810, a Low-Mass Eclipsing Binary in Praesepe Observed by PTF and K2
Theoretical models of stars constitute a fundamental bedrock upon which much
of astrophysics is built, but large swaths of model parameter space remain
uncalibrated by observations. The best calibrators are eclipsing binaries in
clusters, allowing measurement of masses, radii, luminosities, and
temperatures, for stars of known metallicity and age. We present the discovery
and detailed characterization of PTFEB132.707+19.810, a P=6.0 day eclipsing
binary in the Praesepe cluster (~600--800 Myr; [Fe/H]=0.140.04). The
system contains two late-type stars (SpT=M3.50.2;
SpT=M4.30.7) with precise masses (~;
~) and radii (~;
~). Neither star meets the predictions of stellar
evolutionary models. The primary has the expected radius, but is cooler and
less luminous, while the secondary has the expected luminosity, but is cooler
and substantially larger (by 20%). The system is not tidally locked or
circularized. Exploiting a fortuitous 4:5 commensurability between
and , we demonstrate that fitting errors from the unknown spot
configuration only change the inferred radii by <1--2%. We also analyze subsets
of data to test the robustness of radius measurements; the radius sum is more
robust to systematic errors and preferable for model comparisons. We also test
plausible changes in limb darkening, and find corresponding uncertainties of
~1%. Finally, we validate our pipeline using extant data for GU Boo, finding
that our independent results match previous radii to within the mutual
uncertainties (2--3%). We therefore suggest that the substantial discrepancies
are astrophysical; since they are larger than for old field stars, they may be
tied to the intermediate age of PTFEB132.707+19.810.Comment: Accepted to ApJ; 36 pages, 19 figures, 8 tables in two-column AASTEX6
forma
Candidate Isolated Neutron Stars and Other Optically Blank X-ray Fields Identified from the ROSAT All-Sky and Sloan Digital Sky Surveys
Only seven radio-quiet isolated neutron stars (INSs) emitting thermal X rays
are known, a sample that has yet to definitively address such fundamental
issues as the equation of state of degenerate neutron matter. We describe a
selection algorithm based on a cross-correlation of the ROSAT All-Sky Survey
(RASS) and the Sloan Digital Sky Survey (SDSS) that identifies X-ray error
circles devoid of plausible optical counterparts to the SDSS g~22 magnitudes
limit. We quantitatively characterize these error circles as optically blank;
they may host INSs or other similarly exotic X-ray sources such as radio-quiet
BL Lacs, obscured AGN, etc. Our search is an order of magnitude more selective
than previous searches for optically blank RASS error circles, and excludes the
99.9% of error circles that contain more common X-ray-emitting subclasses. We
find 11 candidates, nine of which are new. While our search is designed to find
the best INS candidates and not to produce a complete list of INSs in the RASS,
it is reassuring that our number of candidates is consistent with predictions
from INS population models. Further X-ray observations will obtain pinpoint
positions and determine whether these sources are entirely optically blank at
g~22, supporting the presence of likely isolated neutron stars and perhaps
enabling detailed follow-up studies of neutron star physics.Comment: Accepted for publication in the AJ; higher resolution figures
available at http://www.astro.washington.edu/agueros/pub
The Fifth Data Release of the Sloan Digital Sky Survey
This paper describes the Fifth Data Release (DR5) of the Sloan Digital Sky
Survey (SDSS). DR5 includes all survey quality data taken through June 2005 and
represents the completion of the SDSS-I project (whose successor, SDSS-II will
continue through mid-2008). It includes five-band photometric data for 217
million objects selected over 8000 square degrees, and 1,048,960 spectra of
galaxies, quasars, and stars selected from 5713 square degrees of that imaging
data. These numbers represent a roughly 20% increment over those of the Fourth
Data Release; all the data from previous data releases are included in the
present release. In addition to "standard" SDSS observations, DR5 includes
repeat scans of the southern equatorial stripe, imaging scans across M31 and
the core of the Perseus cluster of galaxies, and the first spectroscopic data
from SEGUE, a survey to explore the kinematics and chemical evolution of the
Galaxy. The catalog database incorporates several new features, including
photometric redshifts of galaxies, tables of matched objects in overlap regions
of the imaging survey, and tools that allow precise computations of survey
geometry for statistical investigations.Comment: ApJ Supp, in press, October 2007. This paper describes DR5. The SDSS
Sixth Data Release (DR6) is now public, available from http://www.sdss.or
The Third Data Release of the Sloan Digital Sky Survey
This paper describes the Third Data Release of the Sloan Digital Sky Survey
(SDSS). This release, containing data taken up through June 2003, includes
imaging data in five bands over 5282 deg^2, photometric and astrometric
catalogs of the 141 million objects detected in these imaging data, and spectra
of 528,640 objects selected over 4188 deg^2. The pipelines analyzing both
images and spectroscopy are unchanged from those used in our Second Data
Release.Comment: 14 pages, including 2 postscript figures. Submitted to AJ. Data
available at http://www.sdss.org/dr
The fourth data release of the Sloan Digital Sky Survey
This paper describes the Fourth Data Release of the Sloan Digital Sky Survey (SDSS), including all survey-quality data taken through 2004 June. The data release includes five-band photometric data for 180 million objects selected over 6670 deg 2 and 673,280 spectra of galaxies, quasars, and stars selected from 4783 deg 2 of those imaging data using the standard SDSS target selection algorithms. These numbers represent a roughly 27% increment over those of the Third Data Release; all the data from previous data releases are included in the present release. The Fourth Data Release also includes an additional 131,840 spectra of objects selected using a variety of alternative algorithms, to address scientific issues ranging from the kinematics of stars in the Milky Way thick disk to populations of faint galaxies and quasars.11 page(s